To meet the demand for wireless data traffic having increased since deployment of 4G (4th-Generation) communication systems, efforts have been made to develop an improved 5G (5th-Generation) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’. The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems. In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The Internet, which is a human centered connectivity network where humans generate and consume information, is now evolving to the Internet of Things (IoT) where distributed entities, such as things, exchange and process information without human intervention. The Internet of Everything (IoE), which is a combination of the IoT technology and the Big Data processing technology through connection with a cloud server, has emerged. As technology elements, such as “sensing technology”, “wired/wireless communication and network infrastructure”, “service interface technology”, and “Security technology” have been demanded for IoT implementation, a sensor network, a Machine-to-Machine (M2M) communication, Machine Type Communication (MTC), and so forth have been recently researched. Such an IoT environment may provide intelligent Internet technology services that create a new value to human life by collecting and analyzing data generated among connected things. IoT may be applied to a variety of fields including smart home, smart building, smart city, smart car or connected cars, smart grid, health care, smart appliances and advanced medical services through convergence and combination between existing Information Technology (IT) and various industrial applications.
In line with this, various attempts have been made to apply 5G communication systems to IoT networks. For example, technologies such as a sensor network, Machine Type Communication (MTC), and Machine-to-Machine (M2M) communication may be implemented by beamforming, MIMO, and array antennas. Application of a cloud Radio Access Network (RAN) as the above-described Big Data processing technology may also be considered to be as an example of convergence between the 5G technology and the IoT technology.
Recently, due to the supply of smart phones, data traffic has rapidly increased. The number of users of smart phones will further increase and application services through the smart phones will become more activated. Accordingly, mobile data traffic is expected to increase much more than now. Particularly, when Machine to Machine (M2M) communication such as communication between a person and a machine and communication between machines that correspond to a new mobile market beyond communication between people is activated, traffic transmitted to an evolved NodeB (eNB) is expected to increase beyond that which can be handled.
Direct communication between devices is spotlighted at present as a technology to solve such problems. The technology called Device to Device (D2D) communication receives attention in both a licensed band used by cellular mobile communication and an unlicensed band used by communication such as wireless LAN.
When the D2D communication is combined with the cellular mobile communication, an increase in traffic capacity and a decrease in overload of the eNB are worthy of notice. That is, when User Equipments (UEs) (or Mobile Stations (MSs)) within the same cell or adjacent cells configure a D2D link therebetween and then directly exchange data through the D2D link without passing through an evolved NodeB (eNB) (or Base Station (BS)), a communication path may decrease from two links (that is, a link from the UE to the eNB and another link from the eNB to another UE) to one link.
A discovery between UEs for D2D communication and various processes for allowing a data communication service are being researched by communication standard groups. The discovery refers to a process which a D2D-enabled UE uses to determine whether another D2D-enabled UE is located close to the D2D-enabled UE. The D2D-enabled UE discovers other neighboring D2D-enabled UEs by using direct UE-to-UE signaling.
In a Frequency Division Duplex (FDD) system, the D2D communication may be performed in an UpLink (UP) frequency band. One of the methods of allocating resources to D2D UEs for transmission uses dedicated signaling between the D2D UE and the eNB. The D2D UE which is interested in transmission makes a request for dedicated resources to the eNB, and the eNB allocates the dedicated resources for transmission to the D2D UE. The resource request and assignment of resources takes place in connected state wherein UE and eNB are connected to each other. If no communication with eNB on data radio bearers is going on then BS can release the connection and UE can use the assigned resources in idle state.
Particularly, D2D resources allocated for the discovery may have been allocated to UEs for a long period through a semi persistent method. When the eNB desires to use the allocated resources for another purpose, a method of releasing the resources is required. Further, when the UE moves to an area of another eNB, a method of releasing the resources by a source eNB is required.